Power threshold and confinement in discharges achieving high-βN H-mode phases on EAST tokamak

Abstract

A series of discharges achieving high-βN(>1.5) H-mode phases were obtained on EAST with both LHW and NBI as the heating power, a tungsten divertor, an unfavorable ▽B×B direction configuration for the L-H transition and a lower toroidal field (BT∼1.6T). The experimental power threshold with the unfavorable direction configuration appeared to be higher than previous results with favorable directions in 2014 and 2015, although the tungsten divertor configurations were believed to benefit the L-H transition compared to a graphite divertor. The proportions of LHW and NBI power modulated the ratio of electron temperature to ion temperature, accompanied with an optimal ratio that caused a minimum Ploss. The WCM might have prolonged the dwell time. The power threshold increased with increasing L∥ and lower OLL lead to lower power threshold. Better energy confinement was observed during the high-βN H-mode phases.